ADU/DADU, valuation and financing

[Matthew Jaeger]

How do I properly value my stake in an ADU development project on my property?

Background: I have property on which I intend to put two more units. The lot is 5950 sq. ft. The lot is situated as the standard 50'-60' by about 100'. It is oriented lengthwise east-west with the street to the west and an alley on the east. The house is less than 1000 sq. ft. and situated about 8'-10' off the alley with carport off-alley. That means an enormous yard on the west facing street-side front. 

I intend to put two more units on the land. Seattle allows one main house with an AADU and then a separate DADU. The current house is small enough to qualify as the DADU. The front yard is huge with plenty space for a new "main" house with an AADU. 

An old and valued friend constructs ADUs and houses. The level of trust is strong so I want to make sure we do this properly. We are working out an agreement for him to finance the build and have his company do the build. My share is based on the value of the land that will be contributed. I intend to offer up 49% of the land so that I retain 3000 sq. ft. along with the original house. Spoils will be proportionally based on his construction/build costs and the value of my land. 

Questions: 

How do I determine my share? 

When is my land value determined? At the beginning of the project? At project completion? At sale of property? 

Should I also collect a bit from allowing the project to happen on my property? He is, after all, getting double profit, on construction with his company and at sale.

There are a lot of other things, but this is the focused issue that I am trying to determine at the moment. 

Thank you for your consideration. 

M